Tests have uncovered oil leaks in the engines of three of Qantas's grounded A380s after one of its superjumbos made an emergency landing last week when an engine exploded mid-flight.

Qantas's six double-decker A380s, the world's newest and largest airliner, were removed from service after a large section of the engine, seemingly including part of a turbine, was blown off on flight QF32 from London to Sydney on Thursday, shortly after it had taken off from Singapore. The plane's wing was damaged and debris dropped on to the Indonesian island of Batam. The plane landed safely back in Singapore.

Engineers conducted eight hours of extensive checks on each Rolls-Royce engine over the weekend and the Qantas chief executive, Alan Joyce, said today they discovered oil leaks in the turbine area of three different aircraft.

"That shouldn't be occurring," he said. "The oil leaks were beyond normal tolerances. So Rolls-Royce and our engineers have looked at what we have gathered as an accepted level and they have passed that threshold."

Joyce said all of the airline's A380s would be grounded for a further 72 hours, said Joyce.

"We are not going to take any risks whatsoever. We want to make sure we have a 100% safe operation."

The three affected engines have been removed for further testing.

The day after the incident Joyce said a "design fault" in the giant Trent 900 engines might have caused the blowout; a view he reiterated last night.

"These are new engines on new aircraft and they shouldn't have these issues at this stage," Joyce said.

Qantas said the second incident was not serious but it triggered a second sell-off in Rolls-Royce shares. The company lost £1.2bn of its value in 48 hours amid fears of a BP-style backlash against the company in the US. Shares in Qantas, which has never had a fatal accident since it start flying jetliners, have fallen 2% since Thursday.

Lufthansa and Singapore Airlines, the other airlines that fly A380s fitted with Trent 900 engines, briefly grounded their planes last week but resumed services after checks.

The Qantas engineers were working with Rolls-Royce, who manufacture and maintain the engines, as well as Airbus.

The A380 went into commercial service three years ago. It has been touted as the most economical, quietest and largest aircraft in the world.